I read somewhere that the definition of insanity was to do something repeatedly, expecting different results each time. And I realized that when you look up "insanity" in the dictionary, the definition should be "a writer."
Before you can understand this, though, you need to understand the emotional trauma writers go through.
Readers have it bad enough, but actually writing those feels-crushing stories is a whole 'nother animal. A reader can't control the outcome of the story. Writers have to make the decisions about how they're going to make their characters suffer. And then they have to be inside their characters' heads, watching and feeling their suffering and knowing they could have prevented it. And they constantly have the carrot dangling in front of them to change their characters' lives- at least reduce their pain.
And then there are the accidents. These tend to happen in character chats, when you make a small sub plot for interest. I tried this last night, and it exploded into a horrible, feels-crushing plot twist. While it was perfect, it was very painful. And then, being in my MC's head at the time, I felt it like she did. It even caused me to have a bout of WID. (Writing Induced Depression- a term coined by Leah K. Oxendine over on her blog.)
And after that ramble, back to my main point. Writers go through this in every story. Crying over wayward charries, wishing they wouldn't turn. Being miserable because our poor MC is. And yet we continue to write, thinking that somehow the results will be different next time.
So, the true definition of insanity is a writer.